<html>
<head>
	<meta charset="UTF-8">
	<meta content="IE=edge" http-equiv="X-UA-Compatible">
	<meta content="initial-scale=1.0, maximum-scale=1.0, user-scalable=no, width=device-width" name="viewport">
	<title>3127：[Usaco2013 Open]Yin and Yang</title>
	<!-- css -->
	<link href="../css/base.min.css" rel="stylesheet">
	<link href="../css/project.min.css" rel="stylesheet">
	
	<!-- favicon -->
	<!-- ... -->
</head>
<body class="page-brand">
	<header class="header header-transparent header-waterfall ui-header">
		<ul class="nav nav-list pull-left">
			<li>
				<a data-toggle="menu" href="#menu">
					<span class="icon icon-lg">menu</span>
				</a>
			</li>
		</ul>
		<a class="header-logo header-affix-hide margin-left-no margin-right-no" data-offset-top="213" data-spy="affix">[Usaco2013 Open]Yin and Yang</a>
		<span class="header-logo header-affix margin-left-no margin-right-no" data-offset-top="213" data-spy="affix">[Usaco2013 Open]Yin and Yang</span>
	</header>
	<nav aria-hidden="true" class="menu" id="menu" tabindex="-1">
		<div class="menu-scroll">
			<div class="menu-content">
				<a class="menu-logo" href="../index.html">BZOJ离线题库</a>
				<ul class="nav">
					<li>
						<a class="waves-attach" data-toggle="collapse" href="#problems">题目</a>
						<ul class="menu-collapse collapse in" id="problems">
							<li>
								<a class="waves-attach" href="../index.html">主页</a>
							</li>
							<li>
								<a class="waves-attach" href="../list.html">题目列表</a>
							</li>
						</ul>
					</li>
					<li>
						<a class="collapsed waves-attach" data-toggle="collapse" href="#about">关于</a>
						<ul class="menu-collapse collapse" id="about">
							<li>
								<a class="waves-attach" href="../about.html">关于此项目</a>
							</li>
						</ul>
					</li>
					
				</ul>
			</div>
		</div>
	</nav>
	<main class="content">
		<div class="content-header ui-content-header">
			<div class="container">
				<h1 class="content-heading">
                [Usaco2013 Open]Yin and Yang                </h1>
                <p>时间限制：10s&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;  空间限制：128MB</p>			</div>
		</div>
		<div class="container">
			<section class="content-inner margin-top-no">
				<div class="row">
					<div class="col-lg-13 col-md-13">
						<div class="card margin-bottom-no">
							<div class="card-main">
								<div class="card-inner">
									
                                <h3>题目描述</h3><p><p></p>
<div>Farns (1 &lt;= N &lt;= 100,000) which are connected by N-1 edges such that he can reach any barn from any&nbsp;</div>
<div>other. Farmer John wants to choose a path which starts and ends at two different barns, such that he</div>
<div>does not traverse any edge twice. He worries that his path might be a little long, so he also wantst</div>
<div>o choose another &quot;rest stop&quot; barn located on this path (which is distinct from the start or the end)</div>
<div>. Along each edge is a herd of cows, either of the Charcolais (white hair) or the Angus (black hair)</div>
<div>&nbsp;variety. Being the wise man that he is, Farmer John wants to balance the forces of yin and yang tha</div>
<div>t weigh upon his walk. To do so, he wishes to choose a path such that he will pass by an equal numbe</div>
<div>r of Charcolais herds and Angus herds-- both on the way from the start to his rest stop, and on thew</div>
<div>ay from the rest stop to the end. Farmer John is curious how many different paths he can choose that</div>
<div>&nbsp;are &quot;balanced&quot; as described above. Two paths are different only if they consist of different setsof</div>
<div>&nbsp;edges; a path should be counted only once even if there are multiple valid &quot;rest stop&quot; locationsalo</div>
<div>ng the path that make it balanced. Please help determine the number of paths Farmer John can cho</div>
<p></p></p><hr/><h3>输入格式</h3><p><p></p>
<div>* Line 1: The integer N.</div>
<div>* Lines 2..N: Three integers a_i, b_i and t_i, representing the two barns that edge i connects. t_i&nbsp;</div>
<div>is 0 if the herd along that edge is Charcolais, and 1 if the herd is Angus.</div></p><hr/><h3>输出格式</h3><p><p>Line 1: One integer, representing the number of possible paths Farmer John can choose from.</p></p><hr/><h3>样例输入</h3><pre>7
1 2 0
3 1 1
2 4 0
5 2 0
6 3 1
5 7 1
INPUT DETAILS: 
There are 7 barns and 6 edges. The edges from 1 to 2, 2 to 4 and 2 to 5 have Charcolais herds along 
them.</pre><hr/><h3>样例输出</h3><pre>1
OUTPUT DETAILS: 
No path of length 2 can have a suitable rest stop on it, so we can only consider paths of length 4. 
The only path that has a suitable rest stop is 3-1-2-5-7, with a rest stop at 2.</pre><hr/><h3>提示</h3><p>没有写明提示</p><hr/><h3>题目来源</h3><p>Gold</p>
								</div>
							</div>
						</div>
					</div>
				</div>
				
				
			</section>
		</div>
	</main>

	<div class="fbtn-container">
		<div class="fbtn-inner">
			<a class="fbtn fbtn-lg fbtn-brand-accent waves-attach waves-circle waves-light waves-effect" data-toggle="dropdown" aria-expanded="true"><span class="fbtn-text fbtn-text-left">Menu</span><span class="fbtn-ori icon">apps</span><span class="fbtn-sub icon">close</span></a>
			<div class="fbtn-dropup">
				<a class="fbtn fbtn-brand waves-attach waves-circle waves-light waves-effect" href="../list.html" target="_self"><span class="fbtn-text fbtn-text-left">题目列表</span><span class="icon">menu</span></a>
				<a class="fbtn fbtn-green waves-attach waves-circle waves-effect" href="../index.html" target="_self"><span class="fbtn-text fbtn-text-left">返回主页</span><span class="icon">home</span></a>
				<a class="fbtn waves-attach waves-circle waves-effect" href="http://www.lydsy.com/JudgeOnline/submitpage.php?id=3127" target="_blank"><span class="fbtn-text fbtn-text-left">提交代码</span><span class="icon">send</span></a>
				<a class="fbtn fbtn-orange waves-attach waves-circle waves-effect" href="http://www.lydsy.com/JudgeOnline/wttl/wttl.php?pid=3127" target="_blank"><span class="fbtn-text fbtn-text-left">试题讨论</span><span class="icon">chat</span></a>
				
			</div>
		</div>
	</div>

	<!-- js -->
	<script src="../js/jquery.min.js"></script>
	<script src="../js/base.min.js"></script>
	<script src="../js/project.min.js"></script>
</body>
</html>